1. Field of the Invention
The invention relates to a method of inspecting district heating pipes, in particular to detect faults on the inside and outside surfaces or in the thickness of the pipes, for example. The faults to be detected can be areas with serious corrosion or cracks, for example. This kind of inspection necessitates a shut-down in order to insert a sensor and to move it along the pipe to be inspected, which is often buried. The sensorxe2x80x94or probexe2x80x94is generally an Eddy current sensor or a video camera permanently connected to the exterior of the pipe by a data transmission cable for acquiring and/or recording information relating to the inspection. An operator on the surface can thus check the state of the pipe as the sensor moves forward. The invention can also be adapted to suit other pipe inspection methods.
2. Description of the Prior Art
Many techniques are currently used to move the sensor in the pipe. One technique consists of mounting the sensor on a support and propelling it by injecting compressed air into the pipe. This technique requires a high compressed air flowrate because the outside diameter of the support is substantially less than the inside diameter of the pipe. This difference in diameters is essential for adaptation to variations in the inside diameter of the pipe. It nevertheless remains relatively difficult to pass the sensor around bends or junctions in the pipe, and the sensor may become jammed, which necessitates opening the pipe to extract it.
Another technique consists of mounting the sensor in a motorized vehicle, known as a xe2x80x9ccrawlerxe2x80x9d, which is introduced into the pipe and moves along it. This kind of vehicle has to carry a high load because it includes a drive system. Also, in order to maintain the sensor that it carries substantially centered relative to the pipe, the vehicle must be able to adapt dynamically to variations in the diameter of the pipe. A motorized vehicle of this kind generally has high development and fabrication costs, requires complex maintenance, and has unsatisfactory service life and reliability.
The object of the invention is to remedy these drawbacks by proposing a method of moving a sensor in a pipe with no risk of jamming and at competitive cost.
To this end, the invention consists of a method of inspecting district heating pipes using a sensor, which method comprises:
introducing a vehicle into the pipe, the vehicle including an uninflated balloon and a pulley in which a cable is inserted;
immobilizing the vehicle in the pipe by inflating the balloon; and
moving the sensor in the pipe by fixing it to one end of the cable and pulling on the other end of the cable to move the sensor toward the immobilized vehicle in order to inspect the pipe;
and in which the vehicle includes a parachute and is propelled in the pipe by introducing into the pipe a fluid under pressure that acts on the parachute, the balloon is deflated when the sensor reaches the vehicle immobilized in the pipe, and the vehicle and the sensor are withdrawn from the pipe by pulling on the end of the cable so that the inspection is carried out during the return travel of the vehicle and the sensor.
With the above method the inspection can be carried out from only one end of the pipe. Also, the mass of the vehicle that is moved by the pressurized fluid is very low and this reduces the risk of jamming in the pipe. The parachute is flexible and adapts continuously to the diameter of the pipe, which makes propulsion by the pressurized fluid more efficient. The balloon is advantageously deflated when the sensor reaches the vehicle immobilized in the pipe, after which the vehicle and the sensor are withdrawn from the pipe by pulling on the end of the cable, and the inspection is carried out during the return travel of the vehicle and the sensor. The ends of the cable can remain outside the pipe during the propulsion of the vehicle to inflate the balloon to immobilize the vehicle when the cable is pulled tight. Carrying out the inspection in this way, during the return travel of the sensor, provides better control of the speed of the sensor, and the length of pipe inspected corresponds to the length of cable introduced into the pipe with the vehicle before pressurizing the pipe.
The invention also relates to a vehicle for implementing the inspection method. The vehicle includes a parachute adapted to be moved in the pipe by a pressurized fluid, an inflatable balloon fixed to the parachute and adapted to be inflated to immobilize the vehicle in the pipe, a pulley adapted to receive a cable to which the sensor is fixed in order to move the sensor in the pipe by pulling on the cable when the vehicle is immobilized in the pipe, and a valve for deflating the balloon including a mechanical actuator which initiates deflation of the balloon when the sensor comes into contact with the vehicle. The vehicle forms a compact and lightweight assembly consisting of simple components and can therefore be manufactured at low cost.
The vehicle advantageously further includes a cartridge of pressurized gas with a trigger adapted to inflate the balloon when the cable is pulled tight and a valve for deflating the balloon including a mechanical trigger. In this way the vehicle is automatically immobilized to form an anchorage as soon as it has traveled a predetermined distance in the pipe.
The invention is described in more detail next with reference to the accompanying drawings, which show an embodiment of the invention by way of non-limiting example.